Signaling system



e t. 30 1924. S p E. F. TRAPP SIGNALING SYSTEM Filed Dec. 2. 1920 3 Sheets-Sheet l n m H 5 @r m w w T Airy.

Sept. 30 1924. Q 1,509,851

E F. TRAPP S IGNALING SYSTEM Fi1(d Dec. 2, 1920 3 Sheets-Sheet ill) Patented Sept. 30, 192.

UNITED STATES PATENT OFFICE.

EDYVIN F. TRAPIP, OF VALLEY STREAM, NEW YORK, ASSIGNOR TO WESTERN ELEG- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SIGNALING SYSTEM.

Application filed December 2, 1920.

To all whom it may concern:

Be it known that I, EDWIN F. Tnarr, a citizen of the United States of America, residing at Valley Stream, in the county of Nassau, State of New York, have invented certain new and useful Improvements in Signaling Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to improvements in signaling systems, and more particularly, to a signaling system which is adapted to apply varying potential to a subscribers telephone line upon which the receiver has inadvertently or otherwise been left off its switchhook. This potential causes the receiver to produce a tone designed to attract the attention of the subscriber to the fact that he should replace his receiver.

I-Ieretofore, it has been proposed to employ so-called howler systems adapted to apply a potential of varying magnitude to a subscribers line when the subscriber has inadvertently left his receiver off the switchhook and to provide for the automatic disconnection of the varying potential immediately following the restoration of the subscribers receiver to its switchhook. The aforesaid systems have, however, in so far as the applicant is aware made no provision for discontinuing the application of the varying potential after a predetermined interval, or for apprising the operator at the trouble desk if at the end of such interval the subscriber does not respond to the howling tone. This latter feature is desirable in that the steady production of a howling tone at the subscribers substation for an indefinite period would be objectionable to the subscriber and further, if the varying potential is automatically continued for only an interval sufficient to attract the subscribers attention it he is within hearing distance of his instrument and is then discontinued, the operator is relieved from supervising the connection and may direct her attention to other duti.es.

It is one of the objects of the invention to provide means for connecting the source of varying potential to a subscribers line whenever the receiver is inadvertently left off its switchhook and for disconnecting the source after a definite interval.

It is a further object of the invention to provide an automatic switching mechanism for connecting the source oi varying poten- Serial No. 427,791.

tial to a subscribers line for a definite interval and to provide means for disconnecting the source whenever the subscriber replaces his receiver on the switchhook.

A further object of the invention is to provide supervising means for supervising the application of the varying potential and a still further object of the invention is to provide operator controlled means for repeatedly applying the source of varying potential to the subscribers line.

A further object of the invention is to provide trunking means for extending a connection from a subscribers line to a trouble operators position.

It is believed that a clearer understanding of the invention may be had from the following description taken in connection with the accompanying drawings in which-Fig. 1 shows the line of a calling subscriber terminating at an automatic exchange in a line switch, a diagrammatical representation oi a district selector switch and office sender at the exchange and a jack ended trunk circuit extending to the trouble desk; Fig. 2 shows the circuits of an operators cord and associated howler apparatus at the trouble desk for connection with the trunk circuit of Fig. 1; and Fig. 3 shows the cord circuit of a monitoring operator at the trouble desk for initially connecting with the subscribers lines which appear to be in trouble.

For a disclosure of the complete organization of circuits, Fig. 2 should be placed beneath Fig. 1 and Fig. 3 beneath Fig. 2.

The invention has been illustrated in connection with an exchange system operating upon a full mechanical basis. A subscribers line L has been illustated terminating in an individual line switch 100 which has access to the district selector switch 150. The subscribers line is equipped with the wellknown substation apparatus, and since the line terminates in an automaticexchange it is also equipped with the usual impulse dial S. The district selector switch 150 has access in the well-known manner to other selector switches (not shown) for extending connections to desired subscribers lines and to special traliic trunk circuits. In Fig. 1 a traiiic trunk circuit 17 5 has been illustrated for extending a connection to the trouble operators desk of the exchange. For controlling the setting of the district selector switch and such other switches as may be employed in the establishment of desired connections, an ofiice register sender mechanism 125, the registers of which are adapted to be set through the operation or the subscribers impulse dial S, is diagrammatically represented by the apparatus enclosed within the dotted lines in Fig. 1. Since the sender mechanism 125, line switch and district selector switch 150 form no essential part of the invention, but enter only inoidently into the disclosure thereof, only such portions of their circuits have been illustrated as is considerednecessary to an understanding of this invention. For a complete disclosure of this apparatus and a full description of the manner in which it functions, reference may be had to the application of O. H. Kopp, Serial No. 465,294, tiled April 28, 1921.

Associated with the office sender mechanism 125 is a link circuit terminating in a jack J atthe sender monitoring position on the trouble desk. In case the calling subscrib'er removes his receiver from its switchhook and then fails to extend a connection, a pernranent signal is displayed before the monitoring operator and the operator then connects a cord circuit such as shown in Fig. 3 with the link circuit for the purpose of challenging the subscriber. The cord circuit of Fig. 3 is not only equipped for establishing such connections with calling lines which appear to be in trouble, but is also arranged for monitoring on connections which have been established to called lines which are in trouble. The central oliice portion of such lines, pending the clearing of the trouble, are connected at the main distributing frame to plugging-up tie lines extending to the operators position and terminating in jacks such as illustrated at J, and the outside portion of such lines are disconnected.

' In view of the fact that the connection incoming to the called line and jack J may be established through automatic switching mechanism, the cord circuit of Fig. 3 is pro vided with n'ilechanism for tripping machine ringing without charging a call against the calling subscriber, and also with a flashing key for recalling an originating operator in the event that the connection has been extended se'mi-automatically through such an operators position. The cord circuit is also provided with coin collection and refund keys to enable the operator to supervise calls which have been initiated from coin box lines.

A further link circuit extends between the sender mechanism and the operators position, Fig. 3, and terminates thereat in jack J to enable the monitoring operator to control the sender to connect the line of a subscriber who does not respond to the opera.- tors challenge, through the district s lector switch 150 to the link circuit 175 extending to the trouble desk. By thus routing trouble calls to the trouble desk through the district selector switch 150, the oiiicc sender mechanism may be disassociated from the connection thus established and made available for regular service, while the trouble operator is attempting to clear up the trouble.

For answering calls incoming over the trunk circuit 175, a cord circuit shown in Fig. 2 is provided. This cord circuit is provided with a key K, which when operated to its talking position connects the operators telephone set shown in Fig. 3 to the cord circuit and when operated into its other position initiates the application of a source of varying potential to the strands of the cord circuit and thus to the calling line. For pro ducing a varying potential a source of current B and interrupter I are provided which are connected in series with the primary winding of transformer 'l. The secondary of transformer T is connected by means of a plurality of taps with a plurality of contacts in one of the banks of the stcp-by-step switching mechanism \V. The stcp-by-stcp mechanism i is or the well-known type and is provided with tour banks of contacts and associated brushes, which brushes are adapted to be driven, when started, through two complete revolutions unless the driving circuitof the switch is iuterru itcd by the nu sponse of the subscriber to the howling tone during the iii-st revolution of the switch. A supervisory lamp is provided for apprising the operator or the condition of the circuits.

In view of the fact that the cord circuits shown in Figs. 2 and 3 may be associated in the same position of the trouble desk, a sin gle operators telephone set 0. T. has been illustrated in Fig. 3 for connection with either cord circuit.

Having in mind the foregoing brief description of the apparatus employed in carrying forward the inventive idea, it is believcd that a clearer understanding of the invention may be had from the following description of its mode of operation. It will be assumed that the calling subscriber on the line L initiates a call by removing his re ceiver from switchhooh and then neglects to operate the dial S. Upon the removal of the receiver from its switchhoolr, the ind'ividual line switch 100 is operated in the well-known manner to extend the subscribers line to an idle district selector switch 150, which thereupon becomes associated with an idle oii icc register sender mechanism in a manner fully set forth in the aforesaid application.

Upon the association of the oilicc sender 125 with the district selector swit :h 1: 0. the sequence switch (not shown) of the district selector switch 150 is advanced in the welllznown mar for extending a dialing oil cuit from the subscribers line I to the windill] lib

ings of the stepping relay 101 of the office sender. This circuit may be traced from grounded battery through the left-hand Winding of steppingrelay 101, conductor 102, the outer armature and back contact of relay 200, conductor 201, the lower right-hand contact of sequence switch cam 103, the lower wiper of line switch 100, thence over the subscribers line, the upper wiper of line switch 100, the lower contact of sequence switch cam 1, conductor 105, the inner armature and back contact of relay 200, conductor 202 and thence to ground through the right-hand winding of stepping relay 101.

lln the manner fully setforth in the afore said application, if following the energization of stepping relay 101, the calling subscriber fails to operate his calling dial S for setting the registers of the sender, a perinanent signal becomes displayed before the monitoring operator whose cord circuit is disclosed in Fig. 3. In response to this permanent signal, the monitoring operator inserts the plug P of her cord circuit in the jack (l.

Upon the insertion'of the plug P in the jack J a circuit is established for the monitoring relay 200, which may be traced from grounded battery through the windings of sleeve relays 300 and 301, the sleeve contacts of plug P and jack J, conductor 302 and thence to ground through the winding of relay 200. Belay 301 is marginally wound and does not-receive sufficient cur rent over the circuit previously traced because of the high resistance of the winding 200 and, therefore, does not energize. Relays 200 and 300, however, energize. Upon the energization of relay 200, the impulse circuit previously traced is opened at the armature contacts of relay 200 and conductors 105 and 201 are thereupon extended through the front contacts of the arinatures of relay 200 over conductors 203 and 204: respectively to the tip and ring contacts of the jack J and thence through the tip and ring contacts of plug P to the tip and ring strands of the monitoring operators cord circuit.

Relay 300, upon energizing, closes at its left-hand armature and front contact a cir cuit for the supervisory lamp 303, but this circuit is immediately opened at the lefthand armature and back contact of supervisory relay 304, since relay 304 now becomes energized over a circuit which may be traced from grounded battery, through its right-hand winding, the right-hand armature and back contact of relay 305, the lower ieft-hand winding of repeating coil 306, the intermediate armature and back contact of relay 307, the ring contact of plug P and thence over the circuit previously traced through the calling subscribers line loop and returning to the tip contact of plug P to the upper armature and back contact of relay 307, the upper left-hand winding of repeating coil 306 and thence to ground at the left-hand armature and back contact of relay 305. The calling subscriber is thus provided with through the winding of supervisory relay -1. 1

Following the insertion of plug P in jack J, the monitoring operator operates the talking key 308 for connecting her set 0. T. with the strands of the cord circuit. The operation of the key closes contact 309 and thereby estal'ilishes a circuit for relay 310, which circuit may be traced from grounded battery, through the left-hand winding of relay 310, conductor 311, the inner righthand armature and back contact of relay 312, key contact 309 and thence to ground at the armature and front contact of relay 304. It is to be noted in this connection that relay 310 and the remaining apparatus en closed within the dotted lines of Fig. 3 are common to all of the cord circuits of the monitoring operators position. Relay 310 upon energizing establishes a circuit for re lay 313, which circuit becomes effective as soon the interrupter cam 31 i advances to such a position as to close its contact 315. The circuit of relay 313 may be traced from grounded battery, through the winding of relay 313, the right-hand armature and back contact of relay 316, the outer right-hand armature and front contact of relay 310, interrupter contact 315 and thence to ground at the normally closed contacts of the armature of relay 317. A locking circuit is also established this time through the righthand winding of relay 310, the front contacts of both of its right-hand armatures, interrupter contact, 315 and thence to ground at the armature contact of relay 317- to insure that relays 313 and 316 function through a complete cycle of operations even if the operator releases the key 308 prior to the completion of such cycle.

Relay 313 upon energizing establishes a locking circuit for itself extending through the winding of relay 316, the armature and front contact of relay 313 and thence to ground at the left-hand armature and front contact of relay 310, but relay 316 does not energize in this circuit since its winding is shunted by a direct connection to ground through its right-hand armature and back contact, the outer right-hand armature and front contact of relay 310, interrupter contact 315 and thence to ground at the armature contact of relay 317. as soon, however, as interrupter cam 31 1 advances to such a position as to open contact 315, the shunt around the winding of relay 316 is opened and relay 316 energizes. Upon its energization, the initial energizing circuit of relay talking current 313 is opened at the back contact of its right-hand armature and a circuit is established for the slow-to-release relay 307, which may be traced from grounded battery through the winding of relay 307, the outer'righ-t-hand armature and front contact of sleeve relay 300, the outer right-hand armature and back contact of relay 312, conductor 318, the right-hand armature and front contact of relay 316, the outer righthand armature and'front contact of relay 310, interrupter contact 315 and thence to ground at the normally closed armature contact of relay 317. This circuit does not become effective until interrupter cam 314 again advances to'such a position as to close the contacts 315.

Upon the energization of relay 307 a moinentary bridge is established across the tip and ring contacts of the plug P and the tip and ring strands of the cord circuit are momentarily opened. This function of relay 307 is without effect at this time. At its lowermost armature and front contact, relay 307 establishes a circuit for relay 319, which. may be traced from grounded battery through the Winding of relay 319, the lower-- most armature and front contact of relay 307 and thence to ground at the left-hand armature and front contact of relay 31G. Relay 319 upon energizing in this circuit closes a locking circuit for itself extending through its right-hand armature and front 7 contact, the normally closed break contacts of the inner left-hand armature of relay 312, the winding of relay 312 and thence to ground at the inner right-hand armature and front contact of sleeve relay 300,, At its left-hand armature and front contact, relay 319 prepares a branch circuit from the winding of relay 307 to the armature of relay 31.7, but without effect at this time.

Relay 312 does not energize at once in the locking circuit previously traced through the winding of relay 319, since its winding is shunted by a connection to ground from the right-hand armature and front contact of relay 319, the lowermost armature and front contact of relay 307 and thence to ground at the left-hand armature and front contact of relay 316. This shunt around the winding of relay 3l2 maintained until relay 307 deenergizes which occurs at a predetermined interval after the opening of the circuit of relay 307 at the contact 315 of interrupter cain 314-.

ll hen the shunt is removed from around the winding of relay 312', relay 312 opens the previously traced locking circuit of relay 319 and closes a new locking circuit for relay 319 extending from ground at contact- 329 of key 308, through the outer left hand armature and front contactof relay 312 to the winding of relay 319 and also closes a locking circuit for itself extending from grounded battery through its inner left hand armature and front contact, its winding and thence to ground at the inner right-hand armature and front contact of sleeve relay 300.

Relay 312 at its outer right-hand armature and back contact opens the circuit previously traced through the winding of relay 307 at its inner right-hand armature and back contact opens the starting circuit previously traced through the left-hand winding of relay 310 and at the front contact of its inner right-hand armature establishes a circuit for the operatofis set connecting relay 320, which circuit may be traced from grounded battery through the winding of relay 320, the front contact and inne right-hand armature of relay 312, contact 309 of key 308 and thence to ground the armature and front contact of supervisory relay 304. Upon the opening of the circuit of relay 310, relay 310 deenergizes and at its left-hand armature and front contact opens the locking circuit of relays 31.3 and 316. The circuits of the conin'ion apparatus of the operators position are now in normal condition having served their purpose of causing the energization of relay 320 and the consequence connection of the operators telephone set to the strands of the cord circuit. The common apparatus is primarily intended for controlling the operation of relay 307 for tripping machine ringing, when the monitoring operator answers on a connection incoming on a plugging up line terminating' in a jack J as will be described hereinafter. Upon the energization of relay 320, the operators telephone set O. T. becomes connected with the right-hand windings of the repeating coil 306 over the arinatures and front contacts of relay 320 and the outermost contacts of the talking key 308.

The operator now challenges the calling subscriber in an endeavor to ascertain from the calling subscriber the reason for the failure to dial a number after having: removed his receiver from its swgilchhook. If the operator receives no response from the calling subscriber, she assumes that the calling line is either in trouble. or thal the calling subscriber has removed his receiver and inadvertently left it 00' its switchhook. The operator will thereupon remove the plug P of her cord circuit from the jack J and reinsert it in the jack J.

Removal of plug P from the jack J opens the circuit previously traced through relays 200 and 300 and these relays deenergize. The deenergization of relay 300 opens the locking circuit of relay 312, which there-- upon deenergizes and opens the circuits of relays 320 and 319. Upon the insertion of the plug P in jack J relays 301 and 300 energize, but their operation at this loo time is without interest.

A. circuit is now established between the otlice sender 125 and the operators cord circuit over 0011* ductors 106 and 10? and in the manner fully set forth in the application of U, K. Kopp, Serial No. 165,29 t, filed April 28, 1921, heretofore referred to. The circuits of the oil fice sender are so adjusted as to cause the setting of the district selector switch 150 through its brush and group selection movements, upon the terminals of the special tratlic trunk 17 5 extending to the trouble desk. The setting off the switch 150 by the sender mechanism 125 is accomplished in the well-known manner with the sender sequence switch (not shown) in positions 2 and 4.

As soon as the brushes of the district selector switch 150 have been. set upon the terminals of traffic trunk 175, the sequence switch (not shown) associated with the districtselector switch 150 advances into position 10 in the well-known manner. The fundamental circuit from the cities sender mechanism is new extended to the windings of trunk relay 108 and may be traced as follows: Grounded battery, the left-hand winding of relay 108, the normally closed cont-acts associated with the upper armature of cut-off relay 109, trunk conductor 110, bank terminal 111 and brush 1.12 of the district selector switch150, the lower contact of sequence switch cam 113, conductor 11 1, the armature and back contact of the No. 0 counting relay 115, the sender sequence switch contact 116 (6), the wind ings of the sender stepping relay 11?, conductor 118, the upper contact of sequence switch cam 119, brush 120 and terminal 121 of the district selector switch 150, trunk conductor 122., the normally closed contacts of the intermediate armature of cut oti relay 109 and thence to round through the right-hand winding of trunk relay 108.

Upon the establishment of this circuit, the

otlice sender sequence switchis advanced out of positions 6 and into position 1 1 in the well-known manner and the sequence switch ot' the district selector switch 150 is advanced out of position 10 and into position 11. From position 11 the sequence switch of the district selector is advanced through successive talking selection positions under the control of the cities sender mechanism 125, and since the district selector switch has been so set by the otlice sender as to extend a connection to an operators position, the sequence switch ot the district selector is arrested in position 1 1-1 As soon as the sequence switch or the district selector leaves position 10 the impulsing leads '105 and 201 are disassociated from the otlice sender mechanism and the conductors 114 and 118 of the fundamental circuit are also disconnected. The circuits of the office sender mechanism thereupon return to normal condition and may be employed for controlling theestablishment of other connections.

i l ith the sequence switch of the district selector 150 in position 1 1., a circuit is now established from grounded battery through the left-hand winding of trunk relay 108 the normally closed contacts of the upper armature of relay 109, trunk conductor 110, bank terminal 111 and brush 112 0:! the district selector switch, the upper contact o't sequence switch earn 113, the winding 01 polarized relay 128, the lower contact of sequence switch cam 119, brush 120 and bank terminal 121 of the district selector switch, trunk conductor 122, the normally closed contacts of the intermediate armature of relay 109 and thence to ground' back contact of make busy relay 135. At

its right-hand armature and front contact, relay 108 closes a circuit for the trunk lamp 126, which may be traced from grounded battery through the slow interrupter 127, the normally closed contacts of the outer right-hand armature of relay 135, the righthand armature and front contact of relay 108 and thence to ground through the trunk lamp 126. Trunk lamp 126 is flashed slowly in this circuit until the operator at the trouble desk answers in on the connection.

The operator at the trouble desk noting the flashing of lamp 126 inserts the plug of an idle howler cord circuit at her position in jack 128 of the trunk circuit with which the flashing lamp 126 is associated, and assuming that the operator is the same operator who initially monitored the connection, she will also withdraw the plug P of her monitoring cord circuit from the ack J thus restoring the circuits of the monitoring cord circuitto normal condition.

Upon the insertion of plug 205 in the jack 128, a circuit is established extending from grounded battery, through sleeve relay 206, sleeve contact of plu 205 and jack 128 and thence to ground through the winding of relay 109. Both sleeve relay 206 and the cut-otli relay 109 energize in this circuit. Relay 109 upon energizing disconnects the windings of trunk relay 108 from conductors 110 and 122 of the trunk circuit.- and connects the conductors 110 and 122 to the tip and ring contacts of the jack 128. Trunk relay 108 is now held energized in a local circuit which may be traced from Relays 108 and 123 energize in this ed battery through the outer right-hand armature and front contact of relay 135, the right-hand armature and front contact of relay 108 and to ground through lamp Relay 135 upon energizing closes a locking circuit for itself extending through its inding, contacts 129 associated with its inner left-hand armature and thence to ground through the disconnect key 130. The make busy relay 135 is thus held energized independently of the cut-off relay 109 until the attendant operator releases it by operating the disconnect key 130. Relay 135 is thus maintained energized to connect a busy ground potential to the multiples of test terminal 131 appearing in the banks of all district selector switches having ac cess to the trunk circuit 175 over a circuit extending to terminal 131 over conductor 132 and the front contact of the inner lefthand armature of relay 135. With make lousy relay 135 energized and trunk relay 108 energized, the circuit previously traced forthe auxiliary signal 121 is opened at the outer left-hand armature and back contact of make busy relay 135 and a new circuit for the auxiliary signal 12% is prepared at the outer left-hand armature and front .contact of relay 135, which circuit does not become effective until after the release of relay 108. At its inner right-hand armature and front contact, relay 135 prepares a circuit from the fast interrupter 133, but since trunk relay 108 is energized at this time, this circuit is not completed through the lamp 126. Should the operator withdraw the plug 205 from the jack 128 following the application of the howler tone to the subscribers line, the calling subscriber having responded to the tone, without opening the disconnect key 130, the circuit through the fast interrupter 133 will become extended through the right-hand armature and back contact of relay 108 to ground through the trunk lamp 126 to flash the lamp 126 rapidly to signal the attendant operator that the key 130 should be opened to release the make busy relay 135 and re move the busy potential from the multiples of terminal 131'.

Upon the insertion of plug 205 in the jack and the energization of sleeve relay 206 in the circuit previously traced, a circuit is established for the supervisory lamp 207, which may be traced from ground through the resistance element 208, lamp 207, the armature and front contact of re lay 206 and thence to battery and ground through the armature and back contact of supervisory relay 209. This circuit, however, is immediately opened at the arn'latuln and back contact of relay 200 since relay 209 immediately becomes energized in a circuit which may be traced troln the non grounded pole of battery, the upper righthand winding of repeating coil 210, conductor 211, the ring contacts of plug 205 and jack 128, the intermediate armature and front contact of relay 109, trunk conductor 122, bank terminal 121 and brush 120 of the district selector switch, the lower contact of sequence switch cam 119, the winding of polarized relay 123, the upper contact of sequence switch cam 113, brush 112 and bank terminal 111 of the district selector switch, trunk conductor 110, the upper armature and front contact of relay 109, the tip contacts of jack 128 and plug 205, conductor 212, the winding of supervisory relay 209 and thence to ground through the lower right-hand winding of repeating coil 210. The current now flowing through the winding of polarized relay 123 at the district selector is in such a direction as to cause the effective encrgizvtirm of relay 123 and the advancement of the sequence switch of the district selector out of position 1! and into position 15, in which latter position a direct talking circuit is established between. the suhscribcfis line and the cord circuit of the trouble operator. At the dis trictselector switch. the talking circuit may be traced through the upper lctt-haml contact of sequence switch cam 10+ and thc lower left-hand contact of sequence switch cam 103. The movement of the scqucncc switch of the district selector out of position 14, disconnects the left-hand windings of repeating coil 134 from the calling line and talking current which was up to (his time supplied to the callin lino llH'nPgYlw the left-hand windings of repeating c il 134 is now supplied tlnrough the lhllll' hnnd windings of repeating coil 210 of the opcrm tors cord circuit. The functioning of the circuits of the district selector as ju t dc scribed is fully set forth in tho pnlenl to F. A. Stearn and F. .l. Scnddcr. No. 393.977. issued November 1. 1921.

The trouble operator may now operale her key K to the left lo connect her set 0. T., disclosed in Fig. 3, to the strands of the cord circuit and may again challenge the calling subscriber. If no response is received she then operates the key K to the right, whereupon a circuit is established for the relay 213, which may be traced from grounded battery, through the armature and front contact of supervisory relay 209, winding of relay 213 and thence to ground at the lowermost alternate contact 21 1 of key K. Relay 213 upon energizing establishes a circuit for lamp 207 extending from grounded battery through the interrupter 215, theouter left-hand armature and front contact of relay 213, the outer right-hand armature and back contact of relay 216, the armature and front contact of sleeve relay 206 and thence to ground through the lamp 207 and resistance element 208. The lamp 207 is flashed in this circuit until either the subscriber responds by hanging up his receiver, or until the step-by-step switch 1*? makes two complete revolutions as will be presently described.

At its right-hand armature and front contact, relay 213 establishes a circuit for the cut-in relay 217, which may betraced from grounded battery through the wind ing of relay 217, the right-hand armature and front contact of relay 213 and thence to ground through brush 238 of the switch W and the normal contact of the bank with which it is associated. Relay 217 upon energizing in this circuit closes a locking cir cuit for itself extending through its inner right-hand armature and front contact and thence to ground through contact 21 1 of key K, thus locking the relay 217 energized in dependently of the switch 1V. At its outer right-hand armature and front contact relay 217 prepares a circuit for the disconnect relay 218 which circuit will be described hereinafter. At its left-hand armature and front contact, relay 217 closes the primary circuit of transformer T. This circuit may be traced from the upper terminal of the primary winding of transfori'ner T, thipugh impedance coil 219, the source of current B, interrupter I, the left-hand armature and front contact of relay 217, the lefthand armature and back contact of relay 218 and thence to the lower terminal of the primary winding of transformer T. Through the operation of interrupter I, current is permitted to flow intermittently in the primary winding T, whereby an alteranting current is produced in the secondary winding of transformer T. Upon the energization of relay 213, a starting circuit for starting the step-by-step switch W closed, which may be traced from grounded battery, through the winding of step ping magnet 220, the armature and back contact of this magnet, conductors 221 and 222, the inner left-hand armature and front contact of relay 213, the left-hand armature and back contact of relay 216, brush 223 and the normal contact of the bank with which it is associated and thence to ground through the interrupter 224 closure of this circuit, magnet 220 advances Upon the the brushes of the switch W one step, whereupon the wipers are automatically advanced through a complete revolution by a new circuit for the stepping magnet 220, which may be traced through the winding of magnet 220, the off normal contacts of the bank associated with the brush 22S, brush 223 and thence to ground through the interrupter 22-1.

As the stepping magnet 220 advances the brushes of. switch JV over their respective banks, the brush 288 engages successive contacts of its bank and thereby connects different portions of the secondary winding of transformer T to the left-hand winding of repeating coil 210. This circuit through the secondary winding of transformer i may be traced from ground through the uppermost alternate contact of key K, the lefthand windings of repeating coil 210, alternate contacts 225 of key K, the secondary winding of transformer T, successive taps from the portions of the secondary winding, successive contacts of the bank associated with brush 238 and thence to ground through brush 238. The current flowing in this circuit which was induced from the primary winding of transformer T is thus repeated from the left-hand winding of repeating coil 210, through the right-hand winding of the repeating coil and thence over the circuit previously traced and through the receiver at the calling subscribers substation and produces therein a howling tone which is divided into two complete cycles during a single movement of brush 238 over its bank or during a half revolution of the step-by-step switch W, each cycle aeginning with a tone of minimum magnitude and increasing to one of maximum magnitude. The tone will always begin with a minimum magnitude, since the primary winding of transformer T is closed only upon the cnergization of relay 217 and relay 217 cannot be energized except when the brush is resting on the normal contact of its bank, which contact immediately precedes the first contact connected to a point in the secondary winding of transformer T, corresponding to the minimum number of secondary turns, or a number of turns which insures the minimum t13111S]11lsion ratio between the windings of the transformer.

Should the calling subscriber in response to the howling tone replace his receiver upon its switchhook before the completion of the first revolution. of the switch W, relay 209 becomes deenergizcd opening the circuit of relay 213, thereby opening the previously traced flashing circuit of the lamp 207 and opening the circuit hereinafter to be de scribed which otherwise would cause a second half revolution of the switch W. The deenergization of relay 209 upon the replacement of the receiver at this time closes a circuit through the back contact of relay 209 for causing the lamp 207 to burn stead ily. The operator is "thus apprised of the fact that the subscriber has immediately responded to the howling tone.

The deenergization of relay 213 upon the response of the subscriber establishes a circuit for the disconnect relay 218, which may be traced from grounded battery through the winding of .relay 218, the outer righthand armature and front contact of relay 217, the right-hand armature and back contact of relay 213, the inner right-hand armature and front contact of relay 217 and thence to ground at contact 21 1 of key K. Belay 218 upon energizing immediately opens the circuit traced through the primary winding of transformer T and thus stops the transmission of the howling tone.

If the subscriber does not replace his receiver at this time, when the brushes of the switch W reach the last contact in their respective banks the following circuits are established; from grounded battery through the winding of relay 226, the armature and back contact of relay 227, the last contact of the uppermost bank of switch and thence to ground through brush 228. Relay 226 upon energizing establishes a locking circuit for itself extending through its winding, the winding of relay 227, the armature and front contact of relay 226 and thence to ground through contact 21 1 of key Relay 227 does not energize in this circuit however until the brush 228 leaves the last contact of its bank as its winding is shunted by the ground connected at brush 228. When relay 227 does become energized 1n series with relay 226, a circuit is prepared for relay 216. A second circuit which was established when the brushes of switch W reached the last contacts of their respective banks may be traced from grounded battery, through the winding of stepping magnet 220, the armature and back contact of magnet 220, conductor 221, the last contact of the bank with which brush 223 is associated, brush 223 and thence to ground through the interrupter 224.

Under the influence of the stepping mag net 220, the brushes ,of switch are ad vanced into normal position, when the cir-- cuit of magnet 220 is again established over conductors 221 and 222, the inner left-hand armature and front contact of rela 213, the left-hand armature and back contact of relay 216, the normal contact with which brush 223 is now in engagement and thence to ground through the interrupter 224:. In the manner previously described, the switch W is now driven through a second half revolution and the variable potential is applied to the calling line through the windings of repeating coil 210. If the calling subscriber replaces his receiver upon the switchhooh during the second half revolution of switch the circuits of the cord circuit function as previously described.

If the receiver is not replaced, however. upon the completion of the second half rcvolution of switch W, a circuit is established for relay 216 as soon as the brush reaches the last contact of its bank. which circuit may be traced from grounded battery through the winding of relay 216, the armature and front contact of relay 227, the last contact of the uppermost haul; of switch iv and thence to ground through brush Relay 21.6 upon energizing in this circuit closes a locking circuit for itself extending from its intermediate armature and front contact and thence to ground through contact 211 of key K, opens at its outer righthand armature and back contact the llashin circuit of lamp 207 and at its left-hand armature and back contact opens the circuit previously traced by means of which the switch V was initially moved out of its normal position. Switch 1V is thus prevented from going through another cycle of operations when it reaches its normal position. hen the brush 223 engages the last terminal of its bank, the previously traced circuit through the winding of magnet 220 is closed for advancing the brushes of the switch into normal position. Following the opening of the flashing circuit of lamp 207. the lamp 207 remains dark, since at this time supervisory relay 209 is still energized over the subscribers line loop, and the operator noting that the lamp 207 is dark is apprised of the fact that the calling subscriber has not responded to the howling tone.

If the operator does not desire to again apply the variable potential to the subscribers line, she then operates the key K into its intermediate position, in which position the secondary winding of the transformer T is disconnected from the left-hand winding of repeating coil 210 and the lock ing circuit previously traced for holding relays 216. 217 and 218 energized is opened and these relays thereupon retract their armatures. When the operator withdraws the plug 205 from the jack 128, the circuits previously traced through relays 206. 209 and 109 are opened and the circuits of the operators cord are then completely restored to normal position.

Upon the deenergization of sleeve relay 109 of the trunk circuit 175, the windings of relay 108 are again connected to trunk condu-ctors 110 and 122 of the trunk circuit, and since at this time relay 135 is energized, the trunk lamp 126 glows steadily. As soon as the trouble is cleared on the subscribers line. either by the subscriber hanging up his receiver or by the outside test man, relay 108 becomes deenergized and the previously traced circuit through interrupter 133 and lamp 120 is closed to flash the lamp 126 rapidly to inform the operator that the trouble has been cleared and, that she should release the connection by throwing key 130 thereby unlocking the make busy relay 135 as previously described.

If the operator desires to reapply the variable potential to the subscribers line following a complete cycle of operations of the switch W, she may do so by again operating the key K to the right when the circuits will function in the manner previously described. If the key K is operated to its intermediate position at any time when the switch W is off normal, a circuit will be closed to insure the return of switch W to normal, which may be traced from grounded battery, through the winding of stepping magnet 220, its armature and back contact, the off normal contacts of the lowermost bank of the switch, brush 229, conductor 230, normal contacts 231 of key K and thence to ground. As soon as switch W reaches normal posi tion, this restoring circuit is opened at the brush 229.

The monitoring operator as hereinbefore stated may employ the cord circuit shown in Fig. 3 for answering calls which have come to her position over a plugging-up line 321 terminating in a jack J. If a subscribers line'is in trouble, the office end of such line is joined to a plugging-up line 321 at the main distributing frame and if a call is extended through a full mechanical eX change to such a line which is in trouble, ringing current from the incoming selector switch applied over the brushes of the final selector switch will operate the ring down relay 322, which will thereupon lock up through its inner left-hand armature and front contact, its left-hand winding and the normally closed contacts associated with jack J, and will establish a circuit for the lamp 323. The monitoring operator noting the illumination of lamp 323 inserts the plug P of her cord circuit in the jack J, whereupon the right-hand winding of relay 322 is disconnected from the tip and ring conductors of the plugging-up line and the locking circuit of the relay 322 is opened at the contacts of the jack. and lamp 323 is thereby extinguished.

A circuit is now established through the sleeve relays 300 and 301 of the operators cord circuit and since the sleeve contact of the jack J is connected directly to ground, both relays 300 and 301 become energized. Relay 301 upon energizing establishes a circuit for relay 305 which disconnects ground from the tip strand of the cord circuit and battery from the ring'strand of the cord circuit and connects battery with the tip strand of the cord circuit through the lefthand winding of relay 304, the left-hand armature and front contact of relay 305, the upper left-hand winding of repeating coil 306 and thence to the tip strand of the cord circuit.

In the manner previously described, the common apparatus associated with the cord circuit functions to cause a momentary energization of relay 307, which momentarily establishes a bridge across the tip and ring contacts of the plug P over a circuit which may be traced from the tip of the plug through the upper armature and front contact of relay 307, conductor 324, the innermost normally closed contacts of flashing key 325,'conductor 326, resistance element 327 and thence to the ring contact of the plug through the intermediate armature and front contact of relay 307. The momentary establishment of this bridge is sufficient to trip machine ringing in the incoming selector switch, but is not of sufficient duration to cause the charging of the call against the calling subscriber. In this respect, these circuits function in substantially the manner described in the application of J. W. Gooderham, Serial No. 427,445 filed November 30, 1920. Following the tripping of machine ringing, the operators telephone set relay 320 becomes energized to connect the op erators telephone set to the strands of the cordcircuit. The operator may then communicate with the calling subscriber to inform him that the desired line is out of order, following which the operator releases the connection at her position by withdraw ing the plug P from the jack J.

If the connection has been established to the operators position semi-automatically through an originating operators position and the monitoring operator desires to recall the originating operator, shemay do so by depressing the flashing recall key 325. Upon the operation of key 325, contact 328 of the key is closed to establish a circuit for the slow-to-release relay 317 Sinceat this time relay 319 is held energized over a circuit extending through the outer left-hand armature and contact of relay 312 and contact 329of the talking key 308, a circuit is now established for relay 307 which. may be traced from grounded battery, through the winding of relay 307, the left-hand armature and front contact of relay 319- thence to ground at the armature and front contact of relay 317. The operation o'l' relay 307 opens the strands of the cord circuit and thereby causes the operation of the supervisory relay at the distant originating operators position. During the energization of relay 307, relay 304 is maintained energized over a circuit extending through its left-hand winding, the left-hand armature and front contact of relay 305 and to ground through the right-hand contact of key 325. A connection between the operators telephone set 0. T. and the originating op erators position is maintained during the energization of relay 307 over conductors 324 and 326, contacts 330 and 331 of key 325 and conductors 332 and 333.

If the monitoring operator desires to col-- lect or refund a coin deposited in the calling su-bscribers coinbox, she may do so by operating either the-coin collection key 334 or the refunding-key 335 respectively. The operation of either of these keys closes a circuit for relay 307 which may be traced from grounded battery through the wincling of relay 307 andthence to ground through the left-hand contacts of key-33 or key If the operatordepresses the coin collection key 334; coin collectioncurrent 'is connected to the tip contact of plugP from the source 336 of collecting current through the winding of pilot relay 337 the right-hand contact of key 334, conductor 32 l,- the upper armature and front contact of relay 307 and thence to the tip of the plug. In asimilar manner by the operationof key 335, current from the source 338 may be connected through the'pilot relay-339 over the righthandcontact of key 335, conductor 324k and to the tip o fiplug P. Since these circuits form no essential part of the present invention, no further 'detailed description of the operation of the cord circuit of Fig. 3 will be given.

In the foregoing description, the invention has been described as applicable to an change i operating upon a full mechanical basis. It is obvious, however, that the howler cord circuit may as readily be employed for applyingvariable potential to a manual subscribers-line for producing a howling tone in the receiver of a subscribers substation which has been inadvertently left off the switchhook, and the invention is to be interpreted to cover either of the aforementioned applications of the invention.

lVhat is claimed is:

1. In a telephone exchange system, a subscribers line, a trunk circuit, means under the'control of said subscribers line for extending a connection from said line,'operator controlled means operative if the calling subscriber removes his receiver from the switchhook and fails to cause the extension of suclrconnectionfor extending a connec tion from said line to said trunk circuit, a source of vary-ing potential, and means for connecting said source operatively with said subscribers line.

2. In a telephone exchange system, a subcribers line, a trunk circuit, means under the control of said subscribersline for extending a connection from said line, operator controlled means operative if the calling subscriber removes his receiver from the tion from said line to said trunk circuit, a cord circuit for connection to said trunk circuit, a source for varying potential associated with said cord circuit, and means for connecting said source opcrativcly with said line.

3. In a telephone exchange system, a subcribers line, a trunk circuit, means under the control of said subscribers line for extendng a connection from said line, means operative if the subscriber inadvertently rcmoves his receiver from the switchhook and fails to cause the extension of such connection for extending a connection from said lint to said trunk circuit, a lamp signal associated with said trunk circuit, means for flaslr ing said lamp upon the seizure of said trunk circuit, a cord circuit for connection with said trunk circuit, a source of varying potential associated with said cord circuit, and means for connecting said source operatively with said line.

4c. In a telephone exchange system, a suhscribe'rs line, a source of varying potential, means including an operators cord circuit for associating said source witlrs'aid line for a predetermined interval, and means under the control of said line for disconnecting said source prior to the expiration of said interval.

5' In a telephone exchange system, a Silliscribers line having associated therewith a substation set in its operated position, a source of varying potential adapted for connection to said line, means including an operators cord circuit for opcratively connecting said source with said line for a predetermined interval, and means under the control of said line for disconnecting said source prior to'the expiration of said interval when said substation is restored to its normal non-operated position.

6. In a telephone exchange system, a sill scribers line having a substation receiver and switchhook, a source of varying potential adapted for connection with said line, means for operatively connecting said source with said line for a predetermined interval if said receiver is inadvertently maintained off said switchliook, means operative upon the replacement of said receiver for disronnecting said source, means for producing a signal during the connection of said source. and means for discontinuing said signal if said receiver has not been replaced at the expiration of said interval.

7. In a telephone exchange system, a subscribers line having a substation receiver and switchhook, a cord circuit for connection therewith, a source of varying potential associated with said cord circuit, operator controlled means for causing the connection of said source with said cord circuit if said receiver is inadvertently maintained oif said switch'hook, means for disconnecting said source after a predetermined interval, means operative upon the replacement of said receiver for disconnecting said source, means for producing a signal before the operator during the connection of said source, and means for discontinuing said signal if the receiver has not been replaced at the expiration of said interval.

8. In a telephone exchange system, a subscribers line having a substation receiver and switchhook, a cord circuit for connection therewith, a source of varying potential associated with said cord circuit, a key for causing the connection of said source with said cord circuit if said receiver is inadvertently maintained off said switchhook, means for disconnecting said source after a predetermined interval, means operative upon the replacement of said receiver for disconnecting said source, means for producing a signal during the connection of said source, and means for discontinuing said signal if said receiver has not been replaced at the expiration of said interval.

9. In a telephone exchange system, a subscribers line having a substation receiver and switchhook, a source of varying potential adapted for connection to said line, means for operatively connecting said source with said line for a predetermined interval if said receiver is inadvertently maintained off said switchhook, means operative upon the expiration of said interval for maintaining the connection of said source for a second predetermined interval if said re-' ceiver is then off the switchhook, means operative upon the expiration of said second interval for disconnecting said source and means operative upon the replacement of said receiver for disconnecting said source.

10. In a telephone exchange system, a subscribers line having a substation receiver and switchhook, a source of varying potential adapted for connection with said line, means for operatively connecting said source with said line for a predetermined interval if said receiver is inadvertently maintained off said switchhook, means operative upon the expiration of said interval for maintaining the connection of said source for a sec ond predetermined interval, means operative upon the replacement of said receiver for disconnecting said source, a signaling device, means for intermittently operating said device during the connection of said source, means for operating said device steadily if the receiver is replaced during said first interval, and means for disconnecting said device if said receiver is not restored at the expiration of said second interval.

11. In a telephone exchange system, a subscribers line having a substation receiver and switchhook, a cord circuit for connection therewith, a source of varying potential associated with said cord circuit, a key for connecting said source with said cord circuit' if said receiver is inadvertently maintained off said switchhook, means for maintaining the connection of said source for a predetermined interval, means operative upon the replacement of said receiver for disconnecting said source, a signaling device, means for operating said signaling device during the connection of said source, means for disconnecting said signaling device upon the expiration of said interval if said receiver has not been replaced, and means operative in response to said signaling device upon repeated operations of said key for repeatedly connecting said source to said line for a predetermined interval.

12. In a telephone exchange system, a subscribers line having a substation receiver and switchhook, a source of varying potential adapted for connection with said line, a step-by-step switch for operatively connecting said source with said line during one operating cycle of said switch if said receiver is inadvertently maintained off said switchhook, means operative thereafter for advancing said switch through a second operating cycle for maintaining the connection of said source if said receiver is then off the switchhook, means operative thereafter for arresting said switch to disconnect said source, and means operative upon the replacement of said receiver for disconnecting said source.

13. In a telephone exchange system, a sub scribers line, a trunk circuit extending to an operators position, means for extending a connection from said line to said trunk circuit, a cord circuit at said operators position for connection with said trunk circuit, a signal for said trunk circuit, means operative upon the seizure of said trunk circuit for operating said signal, manually operable means for releasing said trunk circuit, and means operative upon disconnection of said cord circuit from said trunk circuit for operating said signal in a distinctive manner until said releasing means is operated.

14. In a telephone exchange system, a subscribers line, a trunk circuit extending to an operators position, automatic switching means for extending a connection from said line to said trunk circuit, a cord circuit at said operators position for connection with said trunk circuit, a signal for said trunk circuit, means operative upon the seizure of said trunk circuit for operating said signal, a key associated with said trunk circuit for releasing said switching means, and means operative upon disconnection of said cord circuit from said trunk circuit for operating said signal in a distinctive manner until said switching means is released by the operation of said key.

15. In a telephone exchange system, a subscribers line, a trunk circuit extending to an operators position, auto'inatic switching means for extending a connection from said line to said trunk circuit, a cord circuit at said operators position for connection with said trunk circuit, a signal lamp for said tiflunk circuit, means operative upon the seizure Of said trunk circuit for flashing said lamp, means cpei'ative upon the connecticn of said cord circuit with said trunk circuit tfor endcring 'said trunk .circuit non-selectable and for operating said lamp steadily, a

key for rendering said trunk circuit select able, and nc-ans operative updn disc0nnuction of said cord circuit from said trunk circuit for operating said la np in a distinCtivc manner until said key is operated.

EDWIN F. TRAPP. 

